QUESTION:
What is the "residential" flow rate for swimming pool cartridge filters and how does it differ from sand or DE filtration?

ANSWER:
Filter manufacturers size all three systems in accordance with the National Sanitation Foundation (NSF) Standard 50 "Circulation System Components for Swimming Pools." Those ratings are as follows:

QUESTION:
Why is there such a wide variation in flow for cartridge filters?

ANSWER:
Unlike DE or sand filters where the flow rate needs to be specific to optimize the performance of the filter system, cartridge filters can work at any flow rate. In fact, the lower the flow per square foot, the more efficient the system works.

We suggest that when selling a consumer a replacement cartridge, review your Unicel Replacement Guide to see if an "upgraded surface area" cartridge is available for that system. All upgrades are displayed with the cartridge it is an upgrade for and "upgrade" printed below the part number. For example, on the bottom of page 5 of the Replacement Guide, part C-4637 is identified as an upgrade for part C-4625. C-4637 has 12 more feet of surface area than C-4625 (with all other dimensions the same).